This invention relates in general to a metal etch solution and method and more particularly to an etch solution and method for patterning sequential layers of titanium, nickel, and copper.
A number of metallization systems have been developed for contacting and interconnecting semiconductor devices including diodes, transistors, integrated circuits, and the like. One such metallization system includes sequential layers of titanium, nickel, and copper. The titanium makes a good ohmic contact to the semiconductor material; the nickel provides a barrier layer, and the copper is a good and inexpensive current-carrying material. Fabrication of a semiconductor device requires that the metal be patterned to contact selected device regions. Other portions of the semiconductor device are often passivated or protected by thermally grown or deposited layers of silicon dioxide. Etching the metal layers must be accomplished without seriously etching these regions of silicon dioxide.
There has not heretofore existed a good etchant or method suitable for etching three metal layers, especially sequential layers of titanium, nickel and copper, in a one-step etch process. It has been necessary to etch each of the metal layers in a separate etch solution. The separate etching of each individual layer requires separate etch baths and then rinsing between each etching to prevent contamination of an etch bath with residual etchant from the previous etch bath. This presents problems with preserving the integrity of the etch mask used to define the metal pattern. Caution must also be exercised to avoid oxidation of one metal layer during or after the etching of the above-positioned metal layer. Formation of an oxide interferes with the normal etching of the metal layer.
Accordingly, a need existed to develop an etch solution and method for the one-step etching of sequential metal layers. It is therefore an object of this invention to provide an etch solution for the etching of sequential layers of titanium, nickel, and copper.
It is another object of this invention to provide a one-step method for the etching of sequential layers of titanium, nickel, and copper.
It is still another object of this invention to provide an improved etchant for etching multiple layer metal structures on semiconductor devices.
It is a further object of this invention to provide an improved etch solution and method for patterning multilayer metal systems without adversely affecting underlying silicon dioxide regions.